OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

May 12, 1999

Mr. David Koch
Senior Technical Service Specialist
P.O. Box 622
Reading, PA 19603-0622

Dear. Mr. Koch:

This letter is in response to your March 24, request for clarification of the Occupational Safety and Health Administration's (OSHA's) respiratory protection requirement for employees exposed to crystalline silica. Thank you for your inquiry.

According to 29 CFR 1910.134(a)(1), respiratory protection must be used "in the control of those occupational diseases caused by breathing air contaminated with harmful dusts, fumes, fogs, gases, smokes, sprays, mists, or vapors." Inhaling crystalline silica dust is correlated with the development of silicosis, pneumoconiosis, and other lung diseases. 29 CFR 1910.134(a)(2) states that "Respirators shall be provided by the employer when such equipment is necessary to protect the health of the employee." When engineering controls such as enclosures or ventilation are not feasible, or while such controls are being implemented, respirators must be used to reduce workers' occupational exposure to airborne contaminants.

Because each worker's environment is different, and the amount of occupational exposure to crystalline silica dust varies, an occupational exposure determination should be completed before selecting an appropriate respirator. The minimum respiratory protection for a worker who is working with crystalline silica dust, but is not doing abrasive-blasting, may be an N95 NIOSH-approved respirator. However, the exposure to crystalline silica must not exceed the assigned protection factor of the respirator.

We appreciate the opportunity to provide you with this information. If you require further assistance, please do not hesitate to contact OSHA's Office of Health Compliance Assistance at 202-693-2190.


Richard E. Fairfax
Directorate of Compliance Programs